Amphoteric surface-active agents

ABSTRACT

This invention relates to amphoteric surface-active agents which have extremely powerful inhibitory action against Gram positive bacteria and which are substantially free from metal halide, and, particularly, sodium chloride. These compounds have the general structure: ##EQU1## wherein R is a straight chain alkyl having from 6 to 16 carbon atoms, R&#39; is a lower alkyl, and M is either hydrogen, an alkali metal or an alkylolamine.

This is a division of co-pending application Ser. No. 594,550, filedJuly 9, 1975, which was a continuation-in-part of application Ser. No.429,681, filed Dec. 28, 1973, and now abandoned, which, in turn, was acontinuation-in-part of application Ser. No. 98,144, filed Dec. 14,1970, now abandoned.

This invention relates to amphoteric surface-active agents and theprocess of making such agents from materials commercially available atlow cost; and it particularly relates to surface-active agents of theaforesaid type which are extremely active against Gram positive bacteriaand are substantially free from metal halide, particularly sodiumchloride. They are useful for a variety of purposes.

The products of this invention contains a tertiary amino group attachedto the 2-carbon of a long chain alkyl, and a carboxyethyl groupsubstituent on the nitrogen atom.

The compounds of the invention have in general the structure: ##STR1##wherein R is a straight chain alkyl having from 6 to 16 carbon atoms; R'is a lower alkyl, such as methyl or ethyl; and M is either hydrogen, analkali metal or an alkylolamine radical, such as mono-, di-, ortri-ethanol, or propanol amine radicals.

These compounds may be readily prepared by the reaction of anN-lower-alkyl-N-2 -alkylamine with either acrylonitrile, an acrylate oracrylic acid, and are preferably prepared from alpha-olefins by methodsknown to the art; as for example, those described in U.S. Pat. Nos.3,287,410; 3,287,411; 3,436,420; and 3,497,555. Alternatively, they maybe prepared from 2-alkanols as well as other materials and by otherreaction procedures, although it is preferred to prepare them from thevery cheap and abundant alpha olefins such as are produced by a Zieglertype synthesis by polymerization of ethylene; or by the cracking ofstraight-chain paraffinic hydrocarbons.

Briefly, the procedures include hydrochlorination or hydrobromination inthe presence of a catalyst such as FeCl₃ to produce the corresponding2-haloalkanes in excellent yield; or by sulfating to produce the 2-alkylsulfates. In either case, the intermediate products are then reactedwith methylamine or ethylamine under pressure to yield the correspondingN-lower alkyl N-2-alkylamines.

More specifically, the amphoteric surface-active agents of the presentinvention may be prepared by reacting the aforesaid secondary 2-amineswith, for example, acrylonitrile, followed by hydrolysis of theresulting alkylamino propionitriles to the corresponding N-loweralkyl-N-2-alkylaminopropionic acids, or by saponification with acalculated quantity of base to their alkali metal or alkylolamine salts.Instead of acrylonitrile, acrylic acid or an acrylate, more specificallya lower alkyl acrylate such as ethyl acrylate or the like may besubstituted. Instead of the acrylics, β-propiolactone may be employed.The proportion of the acrylic compound relative to the secondary amineis preferably about mol per mol or a moderate excess of the acrylic. Theexcess speeds the reaction, but is not essential. Reaction withacrylonitrile or methyl or ethyl acrylate may be conducted at atemperature of between 100° and 140°C and at a pressure of between 10psi and 60 psi, as developed; alternatively, the reaction may be carriedout at atmospheric pressure by gradual addition of the acrylic reagentbelow the surface. At about 100°C, the reaction is unnecessarily slow;about 130°C is preferred, to avoid polymerization of the acrylic.

Reaction with acrylic acid may be conducted in aqueous medium at about85°-95°C at atmospheric pressure.

Beta propiolactone reacts with the 2-amines at about 60°-120°C atatmospheric pressure, as shown in the following Example 7.

The products so obtained are of value in a multiplicity of applications.In this respect, because of their efficacy in strongly acid solution,they may be employed in pickling or other metal treating operations.They are also useful textile assistants, either by themselves or withother agents. They may also be used as dye levelers, softeners andwetting agents. In addition, they are effective emulsifying agents.Because of their amphoteric character, they may be combined withquaternary ammonium or with phenolic and other germicides andpesticides. An important aspect of the present invention is theemployment of these products in cosmetic preparations; for example, incombination with sulfated fatty alcohols and the like, they makeexcellent shampoos and bubble baths.

An essential consideration, especially when the product is used incosmetic formulations such as shampoos and the like, is the absence ofmetal salts. There are two reasons for this: (a) metal salts, such assodium or potassium chloride, act as thickening agents in shampoos andthe like; tending to cause significant thickening at concentrations aslow as 0.05 to 2.0% by weight, depending on the system, so that if asurfactant contains, for example, 0.7% and is used in concentrations of30% by weight, the final product would contain 0.2% by weight salt andwould render the product too viscous to provide sufficient flexibilityin the preparation of the desired formulation; and (b) metal salts suchas sodium and potassium chloride are irritants to both the skin and eyesif present in significant proportions, as, for example, above 0.5% byweight.

Prior processes for preparing compounds of this general type haveusually resulted in the formation of excessive metal salts which couldnot be satisfactorily removed. For example, in one such process, theamine is dissolved in ethyl alcohol, heated to 70°-80°C and then reactedwith sodium monochloracetate. Sodium chloride is produced. However, evenwith the greatest care in filtration, applicants could not reduce theconcentration of sodium chloride to less than 2.08% by weight, asdetermined by potentiometer titration with silver nitrate using ametallic silver electrode as the indicator and saturated potassiumsulfate solution as the reference electrode. Even when anhydrous ethanolwas substituted for the normal ethyl alcohol, the sodium chloridecontent could not be reduced to less than 0.7 to 0.8% by weight.

In accordance with the present process, where, for example, anacrylonitrile-amine condensate or an acrylic-ester-amine condensate isused, on hydrolysis the yield is only B-amino acid entirely free ofmetal salt. More specifically, the condensates are hydrolyzed with justenough sodium hydroxide to permit the hydrolyzation to take place. As aresult, sodium chloride production is avoided.

In addition to their surface-active properties, the compounds of thisinvention have extremely powerful inhibitory activity against Grampositive bacteria. Therefore, they may be used in compositions whichrequire an amphoteric surfactant, or inhibition of Gram positivebacteria; and they are particularly useful in compositions where both ofthese properties must reside in one component.

The following examples are illustrative of the present invention,without, however, limiting it except as claimed.

EXAMPLE 1

A crude grade of N-methyl-N-2-tetradecylamine was obtained from alphatetradecene, in the manner taught in U.S. Pat. No. 3,436,420, by thesuccessive steps of hydrochlorinating to 2-chlorotetradecane; and thenaminating with methylamine, and stripping to remove most of thelower-boiling material. The residual product contained some small amountof unreacted olefin and chlorotetradecane, along with traces ofN-methyl-N,N-di(2-tetradecyl) amine. The crude product was reacted witha slight excess of acrylonitrile as follows.

426 grams of the amine or 1.5 mol (by equivalent weight titration) and90 grams or 1.7 mol of acrylonitrile were charged into an agitatedpressure vessel wherein the mixture was heated to 130°-140°C for aperiod of seven hours; the initial pressure was about 60 psi, falling toabout 18 psi towards the end.

Samples were removed at intervals, and were titrated to determine theamount of unreacted acrylonitrile by the mercaptan reaction methoddescribed in American Cyanamid Company's "The Chemistry oAcrylonitrile", (Second Edition, 1959) pgs. 61-62. After three hours,7.3% of residual acrylonitrile was present; after five hours 3.0% andafter seven hours, 2.8%. Conversion was essentially complete toN-methyl-N-2-tetradecyl-amino-beta propionitrile.

Fractional distillation at 2 mm. pressure yielded, after a forerun, a98% pure product in 93% of the theoretical yield, distilling between166° and 180°C.

A repetition of this procedure, but substituting a refined grade ofN-methyl-N-2-tetradecylamine resulted in virtually 100% theoreticalyield. In this respect, either this or the cheaper grade of amine may beemployed for industrial scale applications.

EXAMPLE 2

71.5 grams or 0.25 mol of the 98% grade product of Example 1 was treatedwith 10.2 grams of 98% solid caustic soda in 10 grams of water and 5grams of isopropanol, under reflux in an agitated round-bottom flask fortwo hours, at about 130°C and ambient pressure.

After cooling to 80°C, 70 grams of isopropanol was added, and the refluxcondenser was replaced with a total-take-off condenser. The isopropanolwas distilled off to remove traces of ammonia. After cooling, 150 gramsof water and 40 grams of isopropanol were added. The concentration wasadjusted to 40% active material as the sodium salt ofN-methyl-N-2-tetradecyl-beta-amino propionic acid. This product was aviscous, straw-colored solution having an isoelectric point between 4.5and 6.0.

EXAMPLE 3

In the same manner as in Example 1, the dodecyl-, hexadecyl- andoctadecyl- homologs of N-methyl-N-2alkyl-beta-amino-propionitrile wereprepared from either crude or refined grades ofN-methyl-N-2-alkylamines. Heating times ranged from 7 to 14 hours,temperatures from 110° to 140°C, the pressures varying accordingly. Ineach case, yields of 90%-95% of theory were obtained of products ofabout 99% purity.

EXAMPLE 4

In a similar manner to that of Example 2, the nitriles of Example 3 weresaponified, varying the amounts of alcohol and water, and, consequently,the reflux temperatures and the elapsed time. For example, 3 grams ofthe C₁₂ homolog was saponified with 20 grams of 50% caustic sodasolution and 50 grams of isopropanol at 88°C under reflux for 13 hours:the C₁₆ homolog of 99% purity in the amount of 77.6 grams, with 10.2grams of 98% solid NaOH and 50 grams of ethanol (SD 40) at 84°C for 7hours; and the C₁₈ homolog of 99% purity in the amount of 169.5 gramswith 20.4 grams of 98% solid NaOH, 80 grams of ethanol and 20 grams ofwater at 84°C for 11 hours. The concentration was adjusted to about 40%active material.

EXAMPLE 5

Instead of acrylonitrile, the N-methyl-N-2-alkylamines were reacted withacrylic acid, and also with acrylic esters such as methyl acrylates. Theacrylic acid was inclined to produce small amounts of by-products; theacrylates are exceptionally desirable for their reactioncharacteristics, but are more costly than acrylonitrile. The endproducts are, however, the same. The reaction conditions for such estersas methyl acrylate or ethyl acrylate are substantially the same as foracrylonitrile.

EXAMPLE 6

214 grams of 93% active N-methyl-N-2-dodecylamine (1 mol), 72 grams or 1mol of beta propiolactone and 100 grams each of water and isopropanolplus 53 grams of soda ash were heated together in an agitated,round-bottomed flask under reflux at ambient pressure for five hours atabout 88°-90°C.

The product was a clear, light amber solution which remains completelysoluble in acid and alkaline ranges of pH.

In the same manner the tetradecyl, hexadecyl and octadecyl homologs wereprepared from the corresponding amines, heating from five to sevenhours. All exhibited surface-active properties.

EXAMPLE 7

27 grams (or 0.1 mol) of N-methyl-N-2-hexadecylamine and 7.2 grams (or0.1 mol) of acrylic acid, in 20 grams of distilled water and 15 grams ofisopropanol, was heated under reflux at ambient pressure at about85°-94°C, for 13 hours, to yield a clear, water-soluble product havingsurface-active properties. The other homologous amines reactedsimilarly.

EXAMPLE 8

The alkylaminopropionic acids of the preceding examples may be convertedinto the corresponding amine oxides: ##STR2## by treatment with aperoxide such as hydrogen peroxide, or with ozone. For example, 50.0grams of N-methyl-N-2-hexadecyl-beta-amino-sodium propionate, 40% activesolution, was adjusted to pH 9.7 with hydrochloric acid and 8.0 grams of33% hydrogen peroxide was added, in an agitated round-bottomed flask.The charge was heated at 55°-60°C for three hours, during which time thepH dropped to 7.9 and the residual hydrogen peroxide was negligible.

On cooling, the product was a light colored viscous liquid, gelling atlow temperatures.

In the same manner, 50.0 grams, of a 40% active solution of sodiumN-methyl-N-2-tetradecyl-beta-amino propionate at pH 9.1 was heated with9.1 grams of 33% hydrogen peroxide for two hours at 70°-80°C. The pHdropped to 5.9, and the excess hydrogen peroxide was minimal.

The light colored solution was less viscous than that of the 2-hexadecylhomolog.

EXAMPLE 9

Certain of the above preparations were tested for foaming properties inthe Ross-Miles Foam Tester, at 0.25% active concentration in distilledwater at 104°F, and at three pH levels, 4, 6 and 8. Among those testedwere the 2-dodecyl, 2-tetradecyl and 2-hexadecyl derivatives of Examples2 and 4; and also a 2:1 mixture of the dodecyl and tetradecyl, and 3:1mixture of the tetradecyl and hexadecyl, at 0.25% total activity; theselast being derived from available mixed alpha olefins.

                  Table 1                                                         ______________________________________                                        Sample        pH     Initial  1 Minute                                                                             5 Minutes                                ______________________________________                                        2-dodecyl     4      220       45     0                                         "           6      230      180     5                                         "           8      220      150     15                                      2-tetradecyl  4      225      200    165                                        "           6      235      220    195                                        "           8      230      205    185                                      2-dodecyl/tetradecyl                                                                        4      210      200    150                                       2:1 ratio    6      240      210    120                                                    8      250      210     20                                      2-tetradecyl/hexadecyl                                                                      4      230      210    200                                       3:1 ratio    6      230      210    115                                                    8      235      215    165                                      2-hexadecyl   4      --       --     --                                         "           6      160      135    130                                        "           8      180      150    150                                      ______________________________________                                    

EXAMPLE 10

The foam building or stabilizing properties of the mixed2-dodecyl/2-tetradecyl derivatives in mixture with an equal activeweight of sodium lauryl sulfate, was tested in the Ross-Miles apparatusat 0.1% total active concentration in distilled water at 104°F. Theseparate 2-dodecyl and 2-tetradecyl derivatives and the sodium laurylsulfate were also tested at 0.1% concentration, as well as the latter at0.05% concentration.

                  Table II                                                        ______________________________________                                        ROSS-MILES FOAM HEIGHT IN MILLIMETERS                                         Sample        pH    Initial  1 Minute                                                                             5 Minutes                                 ______________________________________                                        2-dodecyl     6     255      220    215                                       2-dodecyl     8     250      220    215                                       2-tetradecyl  6     210      175    170                                       2-tetradecyl  8     225      190    190                                       2-dodecyl/tetradecyl                                                                        6     240      205    200                                       2-dodecyl/tetradecyl                                                                        8     240      210    200                                       Sodium lauryl sulfate                                                                       6     215      190    185                                         0.1%        8     215      185    180                                       Sodium lauryl sulfate                                                                       6     190      160    160                                         0.05%       8     180      160    160                                       2-hexadecyl   6     160      135    130                                       2-hexadecyl   8     180      150    150                                       ______________________________________                                    

EXAMPLE 11

The products of this invention are effecting wetting agents. Thestandard Draves Wetting Test was applied at pH 6 and pH 8 at 75°F., in0.1% active concentration - in distilled water:

                  Table III                                                       ______________________________________                                        DRAVES WETTING TIME IN SECONDS                                                2-alkyl Component pH6         pH8                                             ______________________________________                                        2-dodecyl         30.1        23.1                                            2-tetradecyl      15.3        8.8                                             Sodium lauryl sulfate                                                                           12.9        11.5                                            ______________________________________                                    

EXAMPLE 12

A typical shampoo formula illustrative of the wide variety of uses wasprepared as follows for the purpose of evaluating the shampooing effecton human hair (percentages are by weight of active content):

    2-alkyl derivative      2.7%                                                  Diethanolamine lauryl sulfate                                                                         11.8                                                  Lauric diethanolamide   5.0                                                   Water to make           100.0                                             

The foaming test showed the following results:

                  Table IV                                                        ______________________________________                                        ROSS-MILES FOAM HEIGHT IN MILLIMETERS                                         2-Alkyl                                                                       Component                                                                              pH    Initial  1 Minute                                                                              5 Minutes                                     ______________________________________                                        2-dodecyl                                                                              6     240      210     205                                           2-dodecyl                                                                              8     235      200     200                                           2-tetradecyl                                                                           6     230      195     195                                           2-tetradecyl                                                                           8     230      200     195                                           ______________________________________                                    

The following procedure was used to test the performance as a shampoo:five gram tresses of natural, brown European human hair, about eightinches in length, were first moistened by holding them under running tapwater at 100°-105°F. An eye-dropper calibrated to contain 1 gram of theagent to be tested was charged with such solution, and this was applieddropwise to the suspended tress, from top to bottom.

A lather was worked up actively between thumb and forefinger, up anddown for one minute; the quality of the lather was noted. The tress wasthen rinsed under running tap water at 100°-105°F. The shampoo and rinsewere repeated a second time. The "Wet Comb Test" comprises combing thetress while wet and observing its manageability. This was repeated afterair-drying overnight, as the "Dry Comb Test". The "Static Test", ameasure of the tendence to develop static, is reported as the spread ininches of the lower end of the trees after such combing, measuring fromthe center to one side of the spread, in inches.

The quality of the lather and the ease of combing were rated as follows:

E = excellent; VG = Very Good; G = Good;

P = poor; VP = Very Poor:

                  Table V                                                         ______________________________________                                        Tress Test at pH 7                                                                                               Static                                     Component                                                                              Lather  Wet Comb  Dry Comb                                                                              Fly-away                                   ______________________________________                                        2-dodecyl                                                                              VG      P         P       1"                                         2-tetradecyl                                                                           VG      VG        E       1/2" - 1"                                  ______________________________________                                    

EXAMPLE 13

The amine oxides of Example 8 were also tested for foaming and wettingproperties, at pH 4, 6, 8 and 10 respectively, in each case at 0.25%active content in distilled water, at 104°F, in the case of theRoss-Miles and at 75°F, in the Draves test.

They performed as follows:

                  Table VI                                                        ______________________________________                                        ROSS-MILES FOAM HEIGHT IN MILLIMETERS                                         2-Alkyl                                                                       Component                                                                              pH     Initial  1 Minute                                                                              5 Minutes                                    ______________________________________                                        2-tetradecyl                                                                           4      190      170     150                                          "        6      160      140     130                                          "        8      25       15      10                                           "        10     115      105     98                                           2-hexadecyl                                                                            4      15       10      10                                           "        6      15       10      10                                           "        8      20       15      15                                           "        10     35       30      30                                           ______________________________________                                    

                  Table VII                                                       ______________________________________                                        DRAVES WETTING TEST                                                           2-Alkyl                                                                       Component     pH           Seconds                                            ______________________________________                                        2-tetradecyl  4            8.3                                                "             6            8.3                                                "             8            12.6                                               "             10           8.8                                                2-hexadecyl   4            17.0                                               "             6            45.8                                               "             8            63.8                                               "             10           56.4                                               ______________________________________                                    

The tetradecyl homolog is suitable as a shampoo additive, as a foambooster or stabilizer and as a hair conditioner. The hexadecyl homologmay be employed in creme rinses, as a skin or hair conditioner; and alsoas a textile conditioner.

The amphoteric surface-active agents of this invention are alsoeffective in other cosmetic preparations; for example, along with analkanolamide, such as "Super-Amide L-9-C" (Onyx Chemical Co.) forbubble-bath formulations; as emulsifying agents, in creams and lotions,and the like.

They are useful auxiliaries in textile processing. In dye baths, theyserve as dye-levelers, penetrating agents, and lubricating agents forall fibers. After dyeing, the lubricating and softening characteristicscarry over to serve to advantage in yarn-winding and sewability, and forall-over reduction of softening agent needed in the finishing operation.

For example, 1% to 2% of a 40% solution on the weight of the fabric,applied in the dyebox, prevents crock-marks, chafe and crow's feet onacetate or rayon. On nylon/cotton, 3% on the weight of the fabricprovides leveling and penetration in dyeing.

For acrylic package pressure dyeing, 5% to 7% on the weight of thefabric serves to provide a more uniform dyeing, the higher percentagesfor light shades, the lower for darker shades.

These amphoterics, and especially those of higher molecular weight,serve at 0.5% to 1.0% add-on as softeners for cotton, rayon and mostsynthetics; with normal fulling agents such as soap they offer a morelubricated "handle", especially on wool.

Since they are amphoteric in nature, they may be used as a self-finish,at 1/2% to 3/4% solids add-on; or they may be used in combination withaminoplast resins as a plasticizer.

They are effective corrosion inhibitors for metals, and hence they maybe incorporated with aerosol formulations. Along with mineral acids suchas, for example, phosphoric, they are useful as metal cleaningcompounds.

They may be compounded with alkalis, including caustic soda and otheragents to make heavy duty industrial cleaning agents. Along with suchother agents as alkylaryl sulfonates, alkanolamides and polyphosphatesor silicates, they may be compounded as all purpose cleaners. With theaid of a thickening agent such as the modified celluloses and an alkali,they make effective over cleaners.

Because of their amphoteric character, they may be combined withquaternary ammonium germicides on the one hand, or with phenols.

The extremely powerful inhibitory action against Gram positive bacteriais demonstrated by the following.

EXAMPLE 14

Sodium N-2-hexadecyl-β-aminopropionate was tested for its ability toinhibit Gram positive bacteria. The minimum inhibitory concentration(MIC) level was determined as follows.

One ml. of aqueous chemical solution prepared at ten times the testconcentration was added aseptically to 9 ml. of sterile nutrient broth.In this manner a series of experimental dilutions of the chemical wasprepared for testing against Staphylococcus aureus. Similarly, a seriesof identical concentration levels in sterile TSB broth was prepared fortesting Streptococcus faecalis.

Each series was inoculated with 0.1 ml. of a 1:10 sterile nutrientbroth, or sterile TSB broth (TSB is Tryptic Soy Broth) dilution of a 24hour broth culture of the test organism. The inoculated broth tubes wereincubated at 37°C for 72 hours, after which the tubes were examined formacroscopic growth.

The absence of growth indicates bacteriostatic activity of thesodium-N-2-hexadecyl-β-aminopropionate. The lowest concentration ofchemical which prevents growth of a bacterial species is designated asthe MIC level of the chemical toward the species. The MIC ofsodium-N-2-hexadecyl-β-aminopropionate toward the two Gram positivebacterial species were as follows:

    S. aureus             10 ppm                                                  S. faecalis           10 ppm                                              

This concentration is considerably lower than the usual acceptableconcentrations for bacterial inhibition. This is a most unexpectedresult.

Their foam-boosting properties for other surfactants and their wettingproperties are amply illustrated in the foregoing Tables.

The invention claimed is:
 1. The compound substantially free from metalhalide having the formula: ##EQU2## wherein R is a straight chain alkylhaving from 6 to 16 carbon atoms, R' is a lower alkyl, and M is selectedfrom the group consisting of hydrogen, alkali metal, mono-, di-, ortri-ethanolamine, and mono-, di-, or tri-propanolamine.
 2. The compoundof claim 1 wherein R' is selected from the group consisting of methyland ethyl.